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Axial ratio and Imepdance Matching

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ankitbende

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Hello everyone,

I am trying to design a circularly polarized patch antenna using probe feed in HFSS. The problem I am facing is the impedance matching of the two orthogonal frequencies generated for circular polarization. I am getting high capacitance for one of the frequency separated by few MHz. Please give me suggestion to nullify this capacitive effect and achieve impedance matching for both the frequencies separated by a little.
I am able to achieve good impedance matching when I increase the outer diameter of coaxial feed in hfss but I have to use standard dimensions of coaxial connector as available in market. Please suggest some method to decrease the capacitance.
 

PlanarMetamaterials

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Hi ankitbende,

I'm not sure what you're referring to. What do you mean by "I am getting high capacitance for one of the frequency separated by few MHz"?
 

ankitbende

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Hello PlanarMetamaterials,

What I am trying to do is achieve axial ratio using single feed, so for that I need to generate two orthogonal frequencies separated by few MHz so that I will get minimum axial ratio in between them. But I am not able to achieve impedance matching for both the two frequencies or you can say over whole band. Attached are the snapshots of S11 and imaginary part of Z. I hope this explains my problem
 

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PlanarMetamaterials

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Hi ankitbende,

Admittedly I still don't understand what you're trying to achieve, but regardless, it seems like your issue is the impedance bandwidth of the patch antenna. Some form of matching can most likely be accomplished at the feed.

Since you are using coaxial connectors, I would attempt to change the radius of the dielectric cutout around the pins which connect to the patch. I've found that this provides a subtle shift in the loading impedance, and may solve your problem.

Good Luck
 

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